Multistage extensible rod antenna

Abstract

A multistage extensible rod antenna system including a plurality of conductive rods which have different diameters, respectively, and are connected in a freely slidable manner to each other. Each of the conductive rods is provided, along its inner circumferential wall of the upper end portion, with first and second stepped portions of different diameters. The first and second stepped portions hold a first collar and a second collar, respectively with an elastic sealing ring therebetween. The upper end face of each of the rods is formed into an engaging portion to keep the collar from slipping off. The multistage extensible rod antenna system thus structured creates less compressive force on the elastic sealing ring, prolonging the elasticity of the sealing ring and extending the service life of the multistage extensible rod antenna system.

I claim: 
     
       1. A multistage extensible rod antenna system comprsing: a multistage extensible rod antenna element including a plurality of conductive rods with respectively different diameters, the conductive rods being connected to each other in a freely slidable manner;   first and second stepped portions of different diameters, the diameter of the first step portion being larger than the diameter of the second step portion, the first and second stepped portions further being formed spaced apart a predetermined distance from each other towards the top on the inner circumferential wall in the upper end portion of each of the plurality of conductive rods;   first and second collars fitted into the first and second stepped portions, respectively, said first collar having a larger outside diameter than said second collar;   an elastic sealing ring fitted between the first and second collars; and   an engaging portion for preventing the collar from slipping off, the engaging portion being formed at the upper end face of each of the plurality of conductive rods.